He and colleagues took brain scans of 13 women and 11 men, aged 19-49 who had volunteered for the study, while they were being sexually stimulated by their partner and during an orgasm and compared them to images of their brains at rest.

'We wanted to know what the brain was doing during orgasm,' Holstege said.

When women genuinely achieved an orgasm, areas of the brain involved in fear and emotion were deactivated. Those areas stayed alert however when women were faking it.

The researchers also found that the cortex, which is linked with consciousness, is active during a fake orgasm but not during the real thing.

'The deactivation of these very important parts of the brain might be the most important thing necessary to have an orgasm,' said Holstege.

'It means that if you are fearful or at a very high level of anxiety, then it is very difficult to have sex because you really have to let yourself go,' he added.

The brain scans for men during orgasm were less conclusive, according to Holstege.

But they did show that different parts of the male and female brain are activated and deactivated during sexual stimulation."